1. Field of the Invention
The present invention is directed to an apparatus for removing air trapped in a bottle bore of a shaft and, more particularly, includes an expandable bladder which displaces the trapped air and allows it travel up the tilted shaft.
2. Description of the Related Art
The present invention is used with an ultrasonic inspection system for inspecting the bore of a turbine or generator rotor shaft. Such an inspection system is described in detail in the above-listed U.S. patents. Such rotors are very large and may be as much as 45 feet in length and several feet in diameter. It is common practice to bore out the center of the shaft to remove flaws in the rotor material. Even after the center of the shaft has been removed, flaws in the steel material near the bore surface may still exist and routine inspections are necessary to determine whether the flaws have expanded due to operating stress and to ensure that the shaft is safe from catastrophic failure.
Immersion type ultrasonic inspection, as practiced in the above-identified U.S. patent applications, requires the use of a liquid such as water as a coupling medium for transmitting ultrasonic pulses from the transducer into the rotor material. Flaws are detected based on reflections of the ultrasonic sound wave from material discontinuities.
A bottle bore shaft is a shaft in which the mid portion has a larger diameter than the end portions. Air can be trapped in the bottle bore portion of the shaft even when the shaft is tilted from a horizontal position. Trapped air reflects and/or diffuses the ultrasonic pulses and the pulse path cannot be reliably determined. Trapped air can prevent the inspection of the portion of the shaft where the air is trapped. For a complete inspection the air must be removed from the shaft.
One method which removes most of the air is described in U.S. Pat. No. 4,670,029 and involves the application of a vacuum to the water filled shaft. Because a perfect vacuum cannot be achieved in the presence of water, about a tenth of the air initially trapped in the bottle bore will remain to form a much smaller air pocket producing a bubble which blocks inspection. FIG. 1 illustrates how a bottle bore 8 can trap air 10 in a water filled 12 shaft 14 even when the shaft 14 is tilted and a vacuum dearation system is used to remove as much air as possible. The water is held in the shaft 14 by an end cap 15.
Another method uses a long small diameter flexible tube at the end of a sensing head to suck the trapped air from the bottle bore. The tube must be attached to a manipulator normally used to position a transducer. This system depends on precise positioning of the tube at the highest point of the surface predicted to harbor the bubble and, since a person cannot actually observe that all the air has been removed, this method does not assure complete removal.
Another much less expensive method uses a flexible vinyl (TYGON) tube attached to the end of a plumbers snake. A small plastic float is attached to the end of a short length of the tube which extends beyond the snake. The snake inserts the tube into the bottle bore where the float lifts the tube into the air pocket where the air is removed by suction. This device is difficult to control and does not assure complete air removal.